This project will assess a variety of biomarkers of age in mice from the domains of behavior and physiology at approximately 150, 450, and 750 days of age. These measures have been selected on the basis and demonstrated age-relevance and genetic influence in addition to meeting standards of biometric adequacy and minimal stress. Most of the measures were employed in a previous research program on the quantitative genetics of aging biomarkers, which provides a valuable interpretational context for the new results on specific quantitative genetics of aging biomarkers, which provides a valuable interpretational context for the new results on specific quantitative trait loci (QTLs). Included are measures of strength and coordination, activity, urine osmolality, blood pressure, and several clinical blood measures. The animals to be employed are of two genetically defined groups: BXD recombinant inbred (RI) strains derived from C57BL/6 and DBA/2 inbred strain and F2 animals derived from the same progenitors. Each group has particular advantages and limitations in the multiple-stage approach to QTL identification and verification, and together offer an advantageous strategy for identifying true QTLs and eliminating from consideration false-positive indications.